Electromagnetic interference (EMI) is a common issue encountered in electronic systems, such as electronic communications systems. Outside electromagnetic radiation is well known to induce undesirable currents in electronic components, thereby disrupting their normal operations. In order to protect against such effects, it is common to completely shield an electronic device or component via highly conductive enclosures, coatings, gaskets, adhesives sealants, wire sleeves, metal meshes or filters, and the like. These types of shields operate by reflecting the unwanted electromagnetic fields away from the sensitive component. Another form of protection is offered by electromagnetic absorbing materials. These are typically not highly conductive and operate by absorbing the unwanted electromagnetic energy and converting it to heat. Absorbers are widely used in radar and stealth applications. They are also commonly found inside of electronic devices where they are used to control electromagnetic emissions from the device. Electromagnetic absorbers can be classified as magnetic absorbers if they interact principally with the magnetic field component of an electromagnetic wave or as dielectric absorbers if the interact principally with the electric field component of the wave.
A variety of different materials and methods have been used to provide EMI shielding. Some of these shielding methods involve non-polymeric matrices. For example, U.S. Pat. No. 3,671,275 (Gates et al.) describes a lossy dielectric attenuator comprised of the combination of silicon carbide and an alumina matrix; U.S. Pat. No. 5,691,498 (Fogle Jr.) describes an electromagnetically lossy liquid- or gas-tight fusion seal constructed of a matrix of glass binder and ferromagnetic and/or ferroelectric filler; and US Patent Publication No. 2010/0294559 (Izawa et al.) describes an electromagnetic shielding film including a laminate of at least an insulating layer and conductive metal layer. Other shielding methods involve polymeric matrices. For example, US Patent Publication No. 2010/0315105 (Fornes) describes an EMI shielding composite comprising a reactive organic compound and conductive filler that during the cure of the organic compound self-assembles into a three dimensional network of metal; and US Patent Publication No. 2011/0200740 (Ma et al.) which describes a carbon nanotube/polymer composite having EMI shielding effectiveness.